I just got one and they are sweet. The barrel is ported for lower rise and recoil, and it's back bored and choked. Vang modifies shotguns for the DEA.

I looked at Hans Vang's work some time ago. an instructor I knew was a littler less than impressed after the low recoil/tactical/flight control etc rounds came out. He convinced me to try the various loads and sure enough, other than the porting effect, the "designated loads" accomplished about the same thing.

Nothing wrong with the Vang ob if you want to be able to increase performance with "standard loads" it does that very well, but with the new loads the standard barrel works fine.